Suspension systems for suspending an object wherein the weight of the object is counterbalanced so that the object can be moved in the gravitational field with apparent weightlessness are well known. They are used extensively for mounting tools, photographic equipment and measuring instruments. The counterbalancing force is provided by many different means. A simple weight suspended from a sheave is the most elementary means of counterbalancing but due to spatial and other limitations it is not always acceptable. Springs and other elastic members have also been used, but they have the disadvantage that the counterbalancing force is not constant over the full extent of their travel. A spring, for example, does not usually have a constant spring force for the various degrees of compression or extension over its range.
It is also known to utilize piston and cylinder assemblies to counteract the weight of an object being suspended. An exemplary prior patent is U.S. Pat. No. 4,000,873, Wallace, issued Jan. 4, 1977. In this patent, a telescoping piston and cylinder arrangement counterbalances the weight of the object.
Another exemplary patent is U.S. Pat. No. 3,917,200, Johnson, issued Nov. 4, 1975. In this device, pneumatic pressure is applied to a cylinder which acts in extension to counterbalance the weight of an object suspended on an arm.
A patent more relevant to the present invention is U.S. Pat. No. 2,225,515, Wood, issued Dec. 17, 1940. In this patent, the patentee suspends a weight directly from the bottom end of the piston within a vertical cylinder, the lower end of the piston being exposed to the atmosphere, the upper end of the piston being exposed to a constant pressure lower than the atmosphere. Wood also provides a specific source of constant fluid pressure below atmospheric utilizing automatic pressure controls. A difficulty with the Wood patent relates to the considerable complexity of the apparatus which maintains the upper chamber of the cylinder at a constant pressure below atmospheric. This apparatus involves pressure-responsive valves, a vacuum pump, various lines, and automatic pressure controls. In view of this considerable complexity, it is clear that it would be of advantage to have a self-contained system capable of providing a relatively constant pressure drop across the piston, regardless of piston position relative to the cylinder and without having to provide an external power source or a pressure-regulating apparatus of the kind utilized by Wood or similar thereto.
The provision of such a simplified but effective system is an object of one aspect of this invention.
The device disclosed herein has a further inventive aspect, relating to the way in which the substantially constant pressure drop across the piston can be transformed into a counterbalancing moment applied to a suspension arm supporting an object at a distance from a horizontal axis, in such a way that the counterbalancing moment diminishes or increases in the same ratio as the moment required to maintain equilibrium thereby keeping the object in place at any angle of the arm. It will be appreciated that, for example, as a suspension arm carrying an object at one end and pivoted at the other end swings down from the horizontal position (representing three o'clock on a clock face) to a downwardly extending position (for example equating to five o'clock on a clock face), the counterbalancing torque necessary to keep the object in place will diminish by a factor which can be expressed in terms of the cosine of the angle through which the swing arm has swung.
It is an object of a further aspect of this invention to provide for this automatic adjustment of the counterbalancing moment arm.
It is an object of a further aspect of the invention to provide an improved device for suspending an object in an easily manoeuvrable manner.
It is an object of yet a further aspect of the invention to provide a counterbalancing device that is effective and inexpensive to make.